Domestic appliance



Oct. 26, 1965 R. D. BREMER DOMESTIC APPLIANCE 2 Sheets-Sheet 1 OriginalFiled Sept. 17 1959 INVENTOR. Robe/f 0 Bremer Attorney 7 I Oct. 26, 1965R. D. BREMER DOMESTIC APPLIANCE 2 Sheets-Sheet 2 Original Filed Sept.17, 1959 4 m F \F INVENTOR. Rober/ 0. Bremer f/ His 142704? UnitedStates Patent Oflice 3,213,522 Patented Oct. 26, 1965 3,213,522 DGMESTICAPPLIANCE Robert I). Bremer, Dayton, Ohio, assignor to General MotorsCorporation, Detroit, Mich, a corporation of Delaware Originalapplication Sept. 17, 1959, Ser. No. 840,715, now Patent No. 3,110,795,dated Nov. 12, 1963. Divided and this application Nov. 28, 1962, Ser.No. 240,623 3 Claims. (Cl. 29155.63)

This invention relates to a domestic appliance and more particularly toan improved method of forming a solid plate cooking unit. This is adivision of my copending application Serial No. 840,715 filed September17, 1959, now Patent 3,110,795 issued November 12, 1963.

The art of electric cooking has long sought a surface cooking unit whichis durable, pleasing in appearance, easy to clean, and able to transmitheat quickly from the electrical resistance element to the cookingutensil or pan. The solid plate cooking unit has been recognizedespecially for its durability and for its ease of cleaning. However, theearly attempts at developing a solid plate cooking unit wereunsatisfactory in that the unit was slow to heat and, with its profuseuse in ceramics, was anything but durable. In the past, it was necessaryto embed an open resistance coil in a channel of powdered dielectric toprotect the coil from the exposed plate. This dielectric packingeliminated the hazard of shock but it also slowed the speed with whichthe unit heated and tended tocrack and dislodge with age, Thus, theelectric cooking art turned from the earlier type solid plate heaters tothe tubular sheathed spirally formed elements now in use. Although thespiral tubular elements provide rapid heat-up they lack even heatdistribution and the convolutions thereof are difiicult to clean. Thisinvention is directed to combining the best attributes of the spiraltubular element into an improved solid plate heater or cooking unit.

Accordingly, it is an object of this invention to provide a compositesolid plate heater having a source of heat therefor sandwiched betweencast top and bottom members.

It is a further object of this invention to provide a method of forminga solid plate cooking unit wherein the plate forming members are castseparately from and prior to their receiving the tubular heatingelement.

A further object of this invention is the provision for using a hightemperature stainless brazing proces for intimately bonding a heatingelement to a solid plate cooking unit casting.

Another object of this invention is the provision of a solid platecooking unit having complementary top and bottom castings to retain aheating element therefor in sandwiched relationship.

A still further object of this invention is the provision of a solidplate cooking unit which may be reversible.

An additional object of this invention is the provision of a method offorming a composite solid plate cooking unit whereby the separatemembers thereof may be bonded in a normal atmosphere furnace.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein preferred embodiments of the present invention areclearly shown.

In the drawings:

FIGURE 1 is a top elevational view of a solid plate cooking unitdesigned in accordance with the concepts of this invention.

FIGURE 2 is a side elevational view of the solid plate cooking unit seenin FIGURE 1.

FIGURE 3 is a fragmentary side sectional view taken along line 3-3 inFIGURE 1 showing the disposition of the heating element terminal ends.

FIGURE 4 is an exploded View of the solid plate cooking unit of thisinvention with one portion being broken away to show a heating elementretaining groove.

In accordance with this invention and with reference to FIGURE 1, asolid plate cooking unit or heater 10 is shown in top elevation. Thecooking unit 10 has a generally circular configuration and is comprisedof a top plate portion 24 and a bottom plate portion 26. The cookingunit 10 derives its source of heat from a tubular heating element 12which is retained partially within the cooking unit in a sandwichedrelationship. The heating element 12 has end portions 14 and 16protruding from the cooking unit 10. The heating element 12 is alsoformed with a stainless steel tubular outer casing which serves as ahousing for a resistance wire, the terminal ends 22 of which areexposed. A dielectric material such as magnesium oxide spaces the wirefrom the tubular casing. The terminal ends 22 of the resistance wireextend slightly from the end of the casing and have Welded thereto spadeor electrical connector members 18 and 20. The utilization of thecooking unit 10 is intended for electric range application at anapproximate operating temperature of 1000 F., and the connecting spades18 and 20 are adapted to be connected to any conventional terminal block(not shown) disposed adjacent the periphery of a range top opening forreceiving the unit. The cooking unit 10 may be controlled in the samemanner by which the present-day spirally formed tubular units arecontrolled. Namely, control may be effected through a temperatureresponsive arrangement whereby the power supply to the heating element12 is proportioned in a given time interval in accordance with a userstemperature selection on an infinite heat switch.

More particularly and with reference to FIGURES 2 and 4, the solid platecooking unit 10 is shown comprised of an upper or top plate member 24and a lower or bottom plate member 26. Dispose-d between the top andbottom members is the heating element 12. It will be noted that thebottom member 26 is formed or cast with a notch or open portion 28 atone point along its periphery to allow the terminal ends 14 and 16 ofthe heating element to project outwardly from between the solid plates24 and 26. For a similar reason, the top plate 24 may be formed or castwith a notch or recess 30 to facilitate a straight generally radiallyoutward projection of the heating element ends 14 and 16 as will bedescribed hereinafter for a reversible unit 10. It should be recognized,however, that the notch '30 may be eliminated in the arrangement of thedrawings where the end portions 14 and 16 of the heating element offsetdownwardly immediately.

For receiving the tubular heating element 12, the bottom plate 26 iscast with a groove 32 which is irregular in conformance with the shapeof the bottom half of the heating element 12. Likewise, a groove 34 iscast into the upper plate member 24 for receiving the top half of theheating element 12. Note that the grooves 32 and 34 are shaped toconfine and conform to the outer sheath of the heating element 12,allowing only for a bonding material 35 between adjacent members tointimately unit these members as will be described more fullyhereinafter.

The method by which the improved solid plate heater may be manufacturedwill now be described. The method comprises a first step whereby twosimilar plates 24 and 26 are cast of a good grade of cast iron. In thisway, a homogeneous casting results which is free of impurities. Ofcourse, it is possible that other materials than iron.-

such as cast stainless steel, may provide the requirements of durabilityand rapid heat transfer essential to solid plate construction. But thewide range of operating temperatures for the unit 14) dictates that theplates 24 and 25 be formed of materials having the same coefficient ofthermal expansion. In this way warpage of the cooking unit at hightemperatures is eliminated. The casting procedure should form thegrooves 32 and 34 as well as the notches 28 and 30 in these castings. Itshould he recognized that the casting process for the simple disc-likeplates 24 and 26 is a simple problem since no heating element is joinedwith or embedded in the plate during the casting process. Further, thefact that the top and bottom castings 24 and 26 for the cooking unit 10are unencumbered with attached or embedded elements permits the castingsto be handled in any manner and treated to any process without theadditional concern for the attached element. For instance, thesecastings could be handled roughly in large quantities and may be platedor surface-treated in any manner suitable to the single material formingthe casting. Although the castings may be sized to any desired formsuitable for use with an electric range, it has been found that a six oreight inch diameter plate such as 24 or 26 having a quarter inchthickness and defining therein grooves having a three sixty-fourths inchradius is suitable for use in the practice of this invention. Themeandering configuration of the grooves 32 and 34 is such as to providethe most effective heat distribution of the heating element within theouter limits of the casting. Thus, for differently sized castings, themeandering or longitudinal configuration of the grooves may necessarilyvary to provide the optimum transfer or conduction of heat to thecasting from the heating element interposed between the castings andfrom the cooking unit to a utensil thereon.

The second step involves coating the entire surface of one of the platesincluding the groove therein with a high temperature stainless brazingcompound (approximately 71% Ni, 16% Cr, 4% Si, 3%% B and 4% Fe), such asNicrobraze, which is sold by the Wall-Colmonoy Company of Detroit,Michigan. This brazing compound comes in a powdered form which may besprinkled dry onto the surface of the plate and the grooves. It is alsosuitable for coating the surfaces to be bonded by being hotsprayed orflame-sprayed to the desired thickness on the plate. Duringflame-spraying, the brazing powder becomes molten droplets whichsolidify upon hitting the plate prior to a subsequent brazing or fusingoperation.

Assuming that the upper plate 24 is selected for the second step, thethird step will encompass the laying or placement of heater 12 in thebrazing compound coated groove 34 of the inverted upper plate 24. Asaforesaid, the groove 34 closely lies in juxtaposition to thecylindrical or tubular shape of the element 12. Next, the exposed halfof the heating element 12 is coated with the brazing compound to ensurethat the heating element 12 will be completely bonded to the grooves 34and 32 of both the top and bottom castings. Although the practice ofthis invention is believed to require a complete coating of brazingcompound on the surfaces to be bonded, it is recognized that the brazingof the exposed surface of the heating element 12 after it is placed inthe first groove 34 might not be necessary due to the sweating action orcapillary attraction which will occur in the furnace during the brazingor fusing operation of the plates 24 and 26 to each other and to theinterposed heating element 12.

At this point, it bears emphasizing that the improved configuration ofthe applicants solid plate heater, improves markedly over thearrangement in the prior art whereby a tubular heating element is simplyattached to a single solid plate or casting. In this prior artsituation, it is necessary to flatten one side of the heating element 12in order to secure enough contact surface for a satisfactory bond, i.e.a surface which is also sufficiently large to transfer the heateffectively from the heating element to the solid plate during cookingoperations. However, in the improved cooking unit of this invention, theutilization of a round or cylindrical cooking tube places approximatelyfifty percent of the element in contact with each of the top and bottomplates. The element 12 is completely surrounded by the metal of thecooking unit 10. This metal rapidly dissipates the heat generated by theelement 12. This characteristic permits the heating element to operateat cooler temperatures than the prior art devices where the tubularelement i simply attached at one point, the remainder being exposed inthe less heat conductive surrounding atmosphere. No flattening isnecessary in the instant article and, thus, the entire manufacturingthereof is simplified in addition to the fact that a superior heattransfer results between the heating element and the solid plates.

After the upper plate 24 and the lower plate 26 are placed in sandwichedrelationship to the heating element 12, and after the brazing compoundhas completely covered the surfaces to be bonded, the assembly is readyfor a fusing operation. For this purpose, a controlled atmospherefurnace is most satisfactory for the brazing operation. Moreparticularly, a dry hydrogen furnace operating at temperatures between1900 F. and 2150 F. may be used to receive the assembly. In the furnacea complete fusing will result wherein the heating element 12 is bondedcompletely to the grooves 32 and 34 and the plates 24 and 26 one to theother along their mating surfaces. It should be noted, however, that thenovel configuration of the applicants cooking unit assembly permits theuse of a normal atmosphere furnace since the sandwiched relationship ofthe assembly necessarily excludes oxygen during brazing. It isimperative that oxidation be prevented if a complete and thorough bondis to occur between the components during the fusing process. A completebond, it should be emphasized, between the plates and between theheating element and the plates is absolutely necessary in order toprevent the heating element from burning out during subsequent cookingoperation.

Lastly, after the furnace brazing operation, the exterior surfaces of acompleted cast iron assembly may be subjected to a protective coatingsuch as a flame spray coating of aluminum or Nicrobraze. However, it isbe lieved to enhance the simplicity of the manufacture if the plates 24and 26 are plated after their casting or formation and prior to thebonding or fusing operation. In this way, the early failure of the unitis resisted since exposure of the heating element 12 to hightemperatures is minimized and the contamination of heating elementdielectric insulation prevented. This plating of the exterior surfacesof a cast iron plate is believed desirable for appearance and to preventundue corrosion of the exposed surface of the cooking unit.

With in the purview of this invention, note also that the terminal ends14 and 16 of the solid plate heater 10 may project directly radiallyoutwardly rather than offsetting downwardly the entire heating element12 laying in a single plane. In such an arrangement, the cooking unit 10is made reversible and adapted to be simply plugged into a receptacle atthe side of the range opening. This permits the simple removal of thesolid plate heater from the range and the transfer thereof to the sinkfor cleaning the unit. Then, too, as one surface of ,the heater 10becomes worn, the unit can be reversed and the appearance life of theproduct doubled. Still further, a reversible application could encompassa top and bottom surface having different characteristics, such as a topsurface plated in a light or bright color and a lower surface in adarker color.

It should now be seen that an improved cooking unit has been taughtwherein a non-interrupted flat surface construction is utilized toprovide even heat distribution. The spirally formed or sheathed tubularheating element of the prior art does not have such heat distribution inview of the point contact of the heating element convolutions with thecooking utensil. In the instant arrangement, the radiation downwardly isminimized, the contact with a pan or utensil on the top surface of thecooking unit serving as the easiest course for the heat conduction. Thesandwiched relationship effects a durable cooking unit, smooth on bothtop and bottom surfaces and thereby easily cleaned. Since the unit isformed of castings, the mass of the unit is considerable and this facttends to minimize warpage of the unit during operation at relativelyhigh temperatures. The fact that the castings or plate members areformed completely separate from the heating element 12 and prior to thefusing of the components enhances the life of the heating element 12 andfurther adds to the overall durability of this solid plate cooking unit.

While the embodiments of the invention as herein disclosed constitutepreferred forms, it is to be understood that other forms might beadopted.

What is claimed is as follows:

1. The method of forming a solid plate heater comprising the steps of,forming a first metal plate having a groove on one surface thereof,forming a second metal plate having a groove complementary to said firstplate groove, coating the grooved side of one of said plates with a hightemperature brazing compound, placing a tubular sheathed heating elementin the groove of one of said plates, coating the sheath of said heatingelement outside the groove of said one of said plates with said brazingcompound, placing the other of said plates in sandwiched relationship tosaid one of said plates and said element to form a sandwiched assemblyexcluding oxygen from the interior thereof, and completely andcoextensively bonding the sheath of said heating element to said firstand second plates and the plates to each other by firing said assemblyin a furnace at temperatures sufiicient to cause said brazing compoundto fuse said first and second plates and said element together.

2. The method of forming a solid plate cooking unit comprising the stepsof, casting a first metal plate of cast iron having a groove of curvedpath on one surface thereof, casting a second metal plate of cast ironhaving the same coefiicient of thermal expansion as the cast iron insaid first metal plate and having a groove complementary to said firstplate groove and a notched portion along the outer periphery thereof,coating the grooved side of said first plate with a high temperaturebrazing compound, placing a cylindrical tubular sheathed heating elementin said first plate groove in a manner to expose a terminal end thereofbeyond said first plate, coating the sheath of said heating elementoutside of said first plate groove with said brazing compound, placingsaid second plate in sandwiched relationship to said first plate andsaid element while positioning said terminal end in said notch to forman assembly, firing said assembly in a furnace at temperatures rangingbetween 1900 F. and 2150 F. completely bonding metallurgically saidfirst and second plates and said element, and then flamespraying abrazing compound which is non-corrosive in normal service on theexterior of said first and second plates to protectively coat theexposed surface of said cooking unit to prevent corrosion thereof.

3. The method of forming a solid plate heater comprising the steps of,forming a first metal plate having a groove of curved path on onesurface thereof, forming a second metal plate having a groovecomplementary to said first plate groove, coating the grooved side ofone of said plates with a high temperature brazing compound, placing atubular sheathed heating element in the groove of one of said plates,coating the sheath of said heating element outside the grove of said oneof said plates with said brazing compound, placing the other of saidplates in sandwiched relationship to said one of said plates and saidelement to form a sandwiched assembly excluding oxygen from the interiorthereof, completely and coextensively bonding the sheath of said heatingelement to said first and second plates and the plates to each other byfiring said assembly in a furnace at temperatures sufiicient to causesaid brazing compound to fuse said first and second plates and saidelement together and protectively plating the exterior of said assemblywith a brazing compound which is non-corrosive in normal service toprevent corrosion of the exposed surfaces of said solid plate heater andto enhance the appearance thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,483,934 10/49Richardson 29-463 2,851,572 9/56 Steck 29-1555 FOREIGN PATENTS 964,0805/57 Germany.

WHITMORE A. WILTZ, Primary Examiner.

JOHN F. CAMPBELL, Examiner.

1. THE METHOD OF FORMING A SOLID PLATE HEATER COMPRISING THE STEPS OF,FORMING A FIRST METAL PLATE HAVING A GROOVE ON ONE SURFACE THEREOF,FORMING A SECOND METAL PLATE HAVING A GROOVE COMPLEMENTARY TO SAID FIRSTPLATE GROOVE, COATING THE GROOVED SIDE OF ONE OF SAID PLATES WITH A HIGHTEMPERATURE BRAZING COMPOUND, PLACING A TUBULAR SHEATED HEATING ELEMENTIN THE GROOVE OF ONE OF SAID PLATES, COATING THE SHEATH OF SAID HEATINGELEMENT OUTSIDE THE GROOVE OF SAID ONE OF SAID PLATES WITH SAID BRAZINGCOMPOUND, PLACING THE OTHER OF SAID PLATES IN SANDWICHED RELATIONSHIP TOSAID ONE OF SAID PLATES AND SAID ELEMENT TO FORM A SANDWICHED ASSEMBLYEXCLUDING OXYGEN FROM THE INTERIOR THEROF, AND COMPLETELY ANDCOEXTENSIVELY BONDING THE SHEATH OF SAID HEATING ELEMENT TO SAID FIRSTAND SECOND PLATES AND THE PLATES TO EACH OTHER BY FIRING SAID ASSEMBLYIN A FURNACE AT TEMPERATURES SUFFICIENT TO CAUSE SAID BRAZING COMPOUNDTO FUSE SAID FIRST AND SECOND PLATES AND SAID ELEMENT TOGETHER.